The sea urchin has an immune system that has some, but not all, of the properties of the vertebrate system. The major features of the sea urchin immunology that will be investigated during the grant period will be: the role of the coelomocytes as mediaters of the immune response, the genetic basis of the immune system memory, and the degree of specificity of the responding system to different tissues and tissue components. In addition, we will be studying the nature of the cell to cell interactions at both the light and electron microscope levels.